Wireless communication system, wireless communication method, wireless LAN access point, and wireless LAN station

ABSTRACT

A predetermined STA includes a station information collection unit collecting from the STA itself and other STAs station information used for selection of STAs performing simultaneous transmission and for control of the simultaneous transmission, and a simultaneous-transmission request unit knowing occurrence of a QoS data frame based on the station information and transmitting a request frame requesting the simultaneous transmission to an AP. The AP includes a station information collection unit; a simultaneous-transmission determination unit selecting a combination of the STAs performing the simultaneous transmission based on the station information by reception of the request frame; and a trigger transmission unit transmitting to each of the STAs performing the simultaneous transmission a trigger frame instructing to performs the simultaneous transmission and including information necessary for controlling the simultaneous transmission. Each of the STAs designated by the trigger frame is configured to simultaneously transmit the wireless frames to the AP.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/547,405, filed Jul. 28, 2017, which is a U.S. National Stageapplication claiming the benefit of prior filed InternationalApplication Number PCT/JP2016/055211, filed on Feb. 23, 2016, in whichthe International Application claims priority from Japanese PatentApplication Number 2015-034352, filed on Feb. 24, 2015, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication system and awireless communication method, in each of which a plurality of wirelessLAN stations transmit wireless frames simultaneously to one wireless LANaccess point, and the wireless LAN access point and the wireless LANstation. In the present specification, the wireless LAN station isabbreviated as “STA”, and the wireless LAN access point is abbreviatedas “AP”.

BACKGROUND ART

Multi-user multiple input multiple output (MU-MIMO) is employed in IEEE802.11ac, which is a wireless LAN standard, in order to efficientlyperform communication in a downlink direction from the AP to the STA. Inthe MU-MIMO, one AP can transmit wireless frames simultaneously to aplurality of STAs. Additionally, in order to efficiently performsimultaneous transmission, a technology is also proposed that flowpairing which is effective when compared with characteristics of trafficis performed.

In Non-Patent Document 1, MU-MIMO in a downlink direction or the like,and a procedure for performing simultaneous transmission or wirelessframes that are exchanged between the AP and STA when performing thesimultaneous transmission are stipulated. Additionally, a procedure isalso stipulated in which combinations of STAs that are destinations ofthe wireless frames which are transmitted with MU-MIMO are grouped, agroup ID (GID) is added to each of the resulting groups of combinations,and then the resulting groups of combinations are simultaneouslytransmitted. In contrast, in Non-Patent Document 2, a groupconfiguration method for performing downlink MU-MIMO that is efficientwhen compared with the characteristics of traffic in the downlinkdirection that can be collected in the AP is disclosed.

On the other hand, in order to perform efficient uplink communicationfrom the STA to the AP, simultaneous transmission in an uplink directionby a plurality of STAs is under study. It is considered that multipleaccess using a space, a frequency, or domains of both makes it possibleto realize the simultaneous transmission of the wireless frames from theplurality of STAs to one AP, but as disclosed in Non-Patent Document 3,this technique is not yet established in a wireless LAN system. However,in Non-Patent Document 4, a procedure is proposed in which the APtransmits wireless frame including information, such as a resourcescheduling, immediately before the plurality of STAs start thesimultaneous transmission and causes the wireless frame to function as atrigger for the simultaneous transmission.

-   Non-Patent Document 1: IEEE802.11ac, “Wireless LAN Medium Access    Control (MAC) and Physical (PHY) Layer Specifications”, December    2013-   Non-Patent Document 2: Y. Inoue, S. Shinohara, M. Mizoguchi, and M.    Morikura, “Flow-Based User Pairing Scheme for Multi-User    Transmissions over WLANs,” Proceedings of the 11th IEEE Vehicular    Technology Society Asia Pacific Wireless Communications Symposium    (APWCS), Ping Tung, Taiwan, Aug. 28-29, 2014-   Non-Patent Document 3: O. Aboul-Magd, “802.11 HEW SG Proposed PAR”,    doc.: 1EEE802.11-14/0165r1, March 2014-   Non-Patent Document 4: Jinyoung Chun, Wookbong Lee, “Uplink    multi-user transmission”, 11-13/1388r0, LG Electronics

Disclosure Problems to be Solved

Although in the plurality of STAs, as disclosed in Non-Patent Document4, the simultaneous transmission in the uplink direction can beperformed using the wireless frame that is the trigger that istransmitted by the AP, it is not guaranteed that the combination of STAsperforming the simultaneous transmission is necessarily for efficienttransmission. For example, when the plurality of STAs perform thesimultaneous transmission, it is expected that communication quality ofeach of the STAs deteriorates much than if a single STA performs thesimultaneous transmission. For this reason, it is desirable that in theSTA that performs the simultaneous transmission, characteristicdegradation due to propagation of the wireless frame is sufficientlyminimized. However, because there is no means of selecting thecombination of STAs, although the plurality of STAs actually perform thesimultaneous transmission, the likelihood that single transmission byeach STA will be an efficient case is considered.

A proposition of the present invention is to provide a wirelesscommunication system and a wireless communication method, in each ofwhich STAs performing simultaneous transmission can be selected and thesimultaneous transmission can be performed on the STAs, when wirelessframes are simultaneously transmitted in a multiple access scheme from aplurality of STAs to one AP, and the wireless LAN station and thewireless LAN access point.

Means for Solving the Problems

According to a first invention, there is provided a wirelesscommunication system in which one AP and a plurality of STAs areconnected to each other, and in which a wireless frame is simultaneouslytransmitted from each of the plurality of STAs to the AP in a multipleaccess scheme, in which the AP includes a station information collectionunit that collects from the plurality of STAs station information whichis used for selection of STAs performing simultaneous transmission andfor control of the simultaneous transmission, asimultaneous-transmission determination unit that selects a combinationof STAs performing the simultaneous transmission based on the stationinformation, and a trigger transmission unit that transmits to each ofthe STA performing the simultaneous transmission a trigger frame whichinstructs to perform the simultaneous transmission and which includesinformation necessary for the control of the simultaneous transmission,and in which each of the STAs that is designated by the trigger frame isconfigured to simultaneously transmit the wireless frame to the AP.

According to the second invention, there is provided a wirelesscommunication system in which one AP and a plurality of STAs areconnected to each other, and in which a wireless frame is simultaneouslytransmitted from each of the plurality of STAs to the AP in a multipleaccess scheme, in which a predetermined STA among the plurality of STAsincludes a station information collection unit that collects from theSTA itself and other STAs station information which is used forselection of STAs performing simultaneous transmission and for controlof the simultaneous transmission, and a simultaneous-transmissionrequest unit that knows occurrence of a Quality of Service (QoS) dataframe based on the station information and that transmits a requestframe requesting the simultaneous transmission to the AP, in which theAP includes a station information collection unit that collects from theplurality of STAs the station information which is used for theselection of the STAs performing the simultaneous transmission and forthe control of the simultaneous transmission, asimultaneous-transmission determination unit that selects a combinationof the STAs performing the simultaneous transmission based on thestation information by reception of the request frame that istransmitted by the predetermined STA, and a trigger transmission unitthat transmits to each of the STAs performing the simultaneoustransmission a trigger frame which instructs to perform the simultaneoustransmission and which includes information necessary for the control ofthe simultaneous transmission, and in which each of the STAs that isdesignated by the trigger frame is configured to simultaneously transmitthe wireless frame to the AP.

In the wireless communication system according to the first invention orthe second invention, in a case when individual CSMA/CA control isperformed on each of the wireless frame destined for the STA and thetrigger frame destined for the plurality of STAs performing thesimultaneous transmission, the AP includes an access control unit thatsets a parameter of CSMA/CA control at which transmission-waiting frameshaving a greater number or transmission-waiting data having a largeramount easily acquires a channel access right, and transmits thewireless frame or the trigger frame that acquired the channel accessright by performing individual CSMA/CA control.

In the wireless communication system according to the first invention orthe second invention, in a case when common CSMA/CA control is performedon each of the wireless frame destined for the STA and the trigger framedestined for the plurality of STAs performing the simultaneoustransmission, the AP includes an access control unit that selects thewireless frame or the trigger frame having a greater number oftransmission-waiting frames or a larger amount of transmission-waitingdata, and transmits the wireless frame or the trigger frame beingselected that acquired the channel access right by performing the commonCSMA/CA control.

According to a third invention, there is provided a wirelesscommunication method in which one AP and a plurality of STAs areconnected to each other, and in which a wireless frame is simultaneouslytransmitted from each of the plurality of STAs to the AP in a multipleaccess scheme, in which the AP includes a first step collecting from theplurality of STAs station information which is used for selection ofSTAs performing the simultaneous transmission and for control of thesimultaneous transmission, a second step selecting a combination of STAsperforming the simultaneous transmission based on the stationinformation, and a third step transmitting to each of the STAsperforming the simultaneous transmission a trigger frame which instructsto perform the simultaneous transmission and which includes informationnecessary for the control of the simultaneous transmission, and in whicheach of STAs that is designated by the trigger frame simultaneouslytransmits the wireless frame to the AP.

According to a fourth invention, there is provided a wirelesscommunication method in which one AP and a plurality of STAs areconnected to each other, and in which a wireless frame is simultaneouslytransmitted from each of the plurality of STAs to the AP in a multipleaccess scheme, in which a predetermined STA among the plurality of STAsincludes a first step collecting from the STA itself and other STAsstation information which is used for selection of STAs performingsimultaneous transmission and for control of the simultaneoustransmission, and a second step knowing occurrence of a Quality ofService (QoS) data frame based on the station information andtransmitting a request frame requesting the simultaneous transmission tothe AP, in which the AP includes a first step collecting from theplurality of STAs the station information which is used for theselection of the STAs performing the simultaneous transmission and forthe control of the simultaneous transmission, a second step selecting acombination of the STAs performing the simultaneous transmission basedon the station information by reception of the request frame that istransmitted from the predetermined STA, and a third step transmitting toeach of the STAs performing the simultaneous transmission a triggerframe which instructs to perform the simultaneous transmission and whichincludes information necessary for the control of the simultaneoustransmission, and in which each of STAs that is designated by thetrigger frame simultaneously transmits the wireless frame to the AP.

In the wireless communication method according to the third invention orthe fourth invention, in a case when individual CSMA/CA control isperformed on each of the wireless frame destined for the STA and thetrigger frame destined for the plurality of STAs performing thesimultaneous transmission, the AP sets a parameter of CSMA/CA control atwhich transmission-waiting frames having a greater number ortransmission-waiting data having a larger amount easily acquires achannel access right, and transmits the wireless frame or the triggerframe that acquired the channel access right by performing individualCSMA/CA control.

In the wireless communication method according to the third invention orthe fourth invention, in a case when common CSMA/CA control is performedon each of the wireless frame destined for the STA and the trigger framedestined for the plurality of STAs performing the simultaneoustransmission, the AP selects the wireless frame or the trigger framehaving a greater number of transmission-waiting frames or a largeramount of transmission-waiting data, and transmits the wireless frame orthe trigger frame being selected that acquired the channel access rightby performing the common CSMA/CA control.

According to a fifth invention, there is provided an AP in a wirelesscommunication system in which one AP and a plurality of STAs areconnected to each other, and in which a wireless frame is simultaneouslytransmitted from each of the plurality of STAs to the AP in a multipleaccess scheme, the AP includes a station information collection unitthat collects from the plurality of STAs station information which isused for selection of STAs performing simultaneous transmission and forcontrol of the simultaneous transmission, a simultaneous-transmissiondetermination unit that selects a combination of STAs performing thesimultaneous transmission based on the station information, and atrigger transmission unit that transmits to each of the STAs performingthe simultaneous transmission a trigger frame which instructs to performthe simultaneous transmission and which includes information necessaryfor the control of the simultaneous transmission.

The AP according to the fifth invention, further includes, in a casewhen individual CSMA/CA control is performed on each of the wirelessframe destined for the STA and the trigger frame destined for theplurality of STAs performing the simultaneous transmission, an accesscontrol unit that sets a parameter of CSMA/CA control at whichtransmission-waiting frames having a greater number ortransmission-waiting data having a larger amount easily acquires achannel access right, and transmits the wireless frame or the triggerframe that acquired the channel access right by performing individualCSMA/CA control.

The AP according to the fifth invention further includes, in a case whencommon CSMA/CA control is performed on each of the wireless framedestined for the STA and the trigger frame destined for the plurality ofSTAs performing the simultaneous transmission, an access control unitthat selects the wireless frame or the trigger frame that having agreater number of transmission-waiting frames or a larger amount oftransmission-waiting data, and transmits the wireless frame or thetrigger frame being selected that acquired the channel access right byperforming the common CSMA/CA control.

According to a sixth invention, there is provided an STA in a wirelesscommunication system in which one AP and a plurality of STAs areconnected to each other, and in which a wireless frame is simultaneouslytransmitted from each of the plurality of STAs to the AP in a multipleaccess scheme, the STA includes a station information collection unitthat collects from an STA itself and other STAs station informationwhich is used for selection of STAs performing simultaneous transmissionand for control of the simultaneous transmission, and asimultaneous-transmission request unit that knows occurrence of a QoSdata frame by the station information and transmits a request framerequesting the simultaneous transmission to the AP.

Effects

According to the present invention, occurrence of a QoS data frame in anSTA makes the STA selected as STAs performing simultaneous transmission,and a plurality of STAs that are announced with a trigger frame canstart the simultaneous transmission in a multiple access scheme at asuitable timing. Additionally, according to the present invention,selection of a combination of STAs that has good data transmissionefficiency of simultaneous transmission can improve throughput of thesimultaneous transmission.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of awireless communication system according to the present invention.

FIG. 2 is a diagram illustrating an example of a configuration of an APand an STA in the wireless communication system according to the presentinvention.

FIG. 3 is a diagram illustrating a control sequence according to a firstembodiment in the wireless communication system according to the presentinvention.

FIG. 4 is a diagram illustrating a control sequence according to asecond embodiment in the wireless communication system according to thepresent invention.

FIG. 5 is a diagram illustrating a control sequence according to a thirdembodiment in the wireless communication system according to the presentinvention.

FIG. 6 is a diagram illustrating a control sequence according to afourth embodiment in the wireless communication system according to thepresent invention.

FIG. 7 is a flowchart illustrating a simultaneous transmission controlprocedure for an AP according to a first embodiment in the wirelesscommunication system according to the present invention.

FIG. 8 is a flowchart illustrating a simultaneous transmission controlprocedure for an AP according to a second embodiment in the wirelesscommunication system according to the present invention.

FIG. 9 is a flowchart illustrating a simultaneous transmission controlprocedure for an STA and an AP according to a third embodiment in thewireless communication system according to the present invention.

FIG. 10 is a flowchart illustrating a simultaneous transmission controlprocedure for an STA and an AP according to a fourth embodiment in thewireless communication system according to the present invention.

FIG. 11 is a diagram illustrating a first configuration of an accesscontrol unit 15.

FIG. 12 is a diagram illustrating a second configuration of the accesscontrol unit 15.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates an example of a configuration of a wirelesscommunication system according to the present invention.

In FIG. 1, one AP and a plurality of STAs, STA 1 to STA n are connectedto each other. A slid line indicates that transmission and reception ofa wireless frame is possible between the AP and each of the STA 1 to STAn. A dashed line illustrates that it is possible that the STA 1 receiveswireless frames that are transmitted by the STA 2 and the STA 3.

FIG. 2 illustrates an example of a configuration of the AP and the STAin the wireless communication system according to the present invention.

In FIG. 2, an AP and an STA each are configured with a wirelesscommunication unit 11 that perform multiple access processing duringtransmission and reception of a wireless frame and simultaneoustransmission, a control unit 12 that performs general control whichincludes control of the transmission and reception of the wirelessframe, an information management unit 13 that manages informationnecessary for each control, a simultaneous transmission determinationunit 14 that collects station information of each STA, determineswhether selection of a combination of STAs performing the simultaneoustransmission and data transmission efficiency of the simultaneoustransmission are good or bad, and generates a trigger frame forannouncing information necessary for control of the simultaneoustransmission to the STAs performing the simultaneous transmission, andan access control unit 15 that acquires a channel access right to awireless frame by performing Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA) control. At this point, wireless framesinclude control signals, such as a downlink data frame that istransmitted by the AP, an uplink data frame that is transmitted by theSTA, station information that is used for the control of thesimultaneous transmission by the STA, an announcement frame, a requestframe, and a trigger frame.

Embodiments will be described below with reference to control sequencesaccording to first to fourth embodiments, which are illustrated in FIGS.3 to 6, and procedure for the control of the simultaneous transmissionaccording to the first to fourth embodiments, which are illustrated inFIGS. 7 to 10.

First Embodiment

FIG. 3 is the control sequence according to the first embodiment in thewireless communication system according to the present invention.

FIG. 7 illustrates Steps S11 to S15 as the procedure for the control ofthe simultaneous transmission according to the first embodiment in thewireless communication system according to the present invention.

In Step S11, the AP collects pieces of station information of the STA 1to STA n necessary for the selection of the STAs performing thesimultaneous transmission and for the control of the simultaneoustransmission and totals collected pieces of station information. Thestation information are traffic information in each STA, or propagationcharacteristic information such as a received power or a channel statusfrom each STA.

Examples of the traffic information in each STA include pieces ofinformation relating to the presence or absence of a transmissionpacket, the numbers of transmission packets, a bit size of thetransmission packet in an access category that has high priority, thepresence or absence of a packet with a threshold or above in atransmission queue, an application type of the transmission packet, ageneration rate of user data that is generated in the STA, the frequencywith which the user data occurs, the presence or absence of thetransmission packet that occurs periodically, and the like. The STAincludes information, such as a packet length of a data frame or anamount of packet bits in an uplink, in the station information, and thuscan cause a length of a Network Allocation Vector (NAV) period to bedecided when the AP sets the NAV that is a period of time for preventionof the packet transmission. In addition, occurrence of traffic in theuplink direction is predicted from an application type of traffic in thedownlink direction from the AP, and thus can be used for the selectionof the combination of the STAs performing the simultaneous transmission.For example, if an application, such as Voice over IP (VoIP), is used,it can be predicted that, when the transmission packet periodicallyoccurs in the downlink direction, the same transmission packet occursalso in the uplink direction. Additionally, during a fixed period oftime, the AP collects a statistical value of uplink traffic on the STA,and predicts the presence and absence of the uplink traffic that occursperiodically, and thus can use results of the collection and predictionfor the selection of the STAs performing the simultaneous transmission.

Furthermore, when a plurality of STAs perform the simultaneoustransmission, more deterioration in communication quality of each of theSTAs is expected than compared with a case of transmitting STA alone.Therefore, when conducting simultaneous transmission, it is desirable tocombine STAs in which characteristic degradation due to propagation ofwireless frames to become sufficiently small. Results of predictingquality of propagation channel between the STA and the AP from areceived-power value of a frame transmitted by the STA, or thecharacteristics between each of the plurality of STAs are compared witheach other, in order to determine this propagation characteristic, andstation information on whether the STAs that have equal receiving powervalues when performing the simultaneous transmission are present or notcan also be used for the determination of the simultaneous transmission.

At this point, as a method of collecting the station information, it ispossible to employ a method in which a frame including the stationinformation is caused to be transmitted periodically or voluntarily fromeach STA, a method in which the STAs are caused to make replay in orderaccording to polling by the AP, a method in which the stationinformation is caused to be carried in the uplink data frame from eachSTA, or a method in which the station information is caused to becarried, as a response frame corresponding to the downlink data frame,for example, in an ACK. If the station information is included in theuplink data frame, the station information is included in data framesfor multiple-user simultaneous transmission in the uplink direction, andthus the AP can continuously perform the simultaneous-transmissioncommunications for a plurality of users according to the presentinvention. Furthermore, information within a QoS control field that isstipulated in IEEE 802.11e may be used to know that a QoS data frameoccurs in the STA. Furthermore, a network other than a wireless LAN,such as a mobile network or a wired network, may be used to collect thestation information in the background. For example, IEEE 802.11k or thelike, or other information exchange sequences may be utilized.

It is noted that an aspect is that not only may pieces of stationinformation of all the STAs be collected in the AP, but also only theSTA which has the uplink traffic transmits the station information tothe AP. Furthermore, an aspect is that, if a predetermined STA collectspieces of station information of other STAs as in third and fourthembodiments that will be described below, only station information ofSTAs that the predetermined STA is capable of hearing may be collected.

Next, in Steps S12 and S13, the AP selects the combination of STAsperforming the simultaneous transmission based on the collected stationinformation, calculates data transmission efficiency of the simultaneoustransmission, and determines whether the calculated data transmissionefficiency is good or bad. Before it comes to the calculation of thedata transmission efficiency, a combination of STAs that have highsimilarity is selected based on a frame size of the uplink traffic thatoccurs in each STA, an interval at which a transmission packet occurs,an access category of the transmission packet, propagationcharacteristic, a data rate that is decided from a transmissioncapability of each of the STAs, and the like, and the data transmissionefficiency of the simultaneous transmission that result from thecombination of STAs is calculated. Then, compares the data transmissionefficiency of the simultaneous transmission by the selected combinationof STAs with the data transmission efficiency by a single STA, and if avalue of the former is high, it is determined that the data transmissionefficiency of the simultaneous transmission is good. Alternatively, theAP compares the data transmission efficiency of the simultaneoustransmission by the selected combination of STAs with a predeterminedthreshold, so that the AP may determine whether the data transmissionefficiency of the simultaneous transmission is good or bad.

As a result, if the data transmission efficiency of the simultaneoustransmission is not good, in Step S14, the AP may not perform thecontrol of the simultaneous transmission in the uplink. On the otherhand, if it is determined that the data transmission efficiency of thesimultaneous transmission is good, in Step S15, the AP generates atrigger frame TRG instructing to perform the uplink simultaneoustransmission to the selected STAs performing the simultaneoustransmission, performs carrier sensing under the CSMA/CA control toacquire the channel access right, and then transmits the trigger frame.

It is noted that during channel access right acquisition processing inStep S15, processing may be performed that assumes the time that ittakes for a request-to-send (RTS) and clear-to-send (CTS) frame in theCSMA/CA control to be transmitted and received and for the selected STAsto complete the simultaneous transmission, sets the NAV which preventsother STAs from performing the transmission, and so forth.

In the trigger frame transmitted by the AP which acquired, the channelaccess right are the combination of STAs performing the simultaneoustransmission selected based on the station information collected todetermine the simultaneous transmission, wireless communication resourceinformation available for each STA, and information necessary foradjusting frequency and timing are included. Moreover, in the triggerframe, for example, a modulation method performing the simultaneoustransmission and penalty information for decreasing a coding rate mayalso be included.

The STAs that is instructed to perform the simultaneous transmissionwith the trigger frame transmitted by the AP, for example, the STA 1 toSTA n that are illustrated in FIG. 3, performs the simultaneoustransmission based on information that is designated, using any one ofFrequency Division Multiple Access (FDMA), Spatial Division MultipleAccess (SDMA or MU-MIMO), and other Multiple Access, or using acombination of these.

Incidentally, the AP transmits the downlink data frame to the STA afterthe channel access right is acquired based on the CSMA/CA control.Therefore, in the access control unit 15 of the AP that is illustratedin FIG. 2, an adjustment needs to be made to the CSMA/CA control for thetransmission of the downlink data frame and the CSMA/CA control for thetransmission of the trigger frame instructing to perform thesimultaneous transmission of the uplink data frame.

At this point, if priority control in accordance with the accesscategory is performed on the downlink data frame, a configuration isconsidered in which the priority control in accordance with the accesscategory of the uplink data frame that is simultaneously transmitted isperformed also on the trigger frame. This priority control in accordancewith the access category is performed by setting a parameter of theCSMA/CA control.

In Enhanced Distributed Channel Access (EDCA) control that results fromenhancing the CSMA/CA control, the AIFS time in accordance with theaccess category AC is used instead of the DIFS time which is the timeuntil determining that the channel is in the idle state. For example,the AIFS time is set shorter for access categories with higher priority.CW_(min) that is a minimum value of a Contention Window (CW) thatdecides a random backoff value of collision avoidance, and CW_(max) thatis a maximum value are also set in accordance with the access category.For example, the higher priority the access category has, the smallervalue CW_(min) and CW_(max) are set to. Furthermore, TransmissionOpportunity (TXOP) that is a parameter that indicates a period of timefor which a channel is used exclusively after the channel access rightis acquired is also set according to the access category. For example,as a priority of the access category become higher, the value of TXOPbecomes larger and the number of frames that can be transmitted afterthe acquisition of the channel access right increases.

If AIFS, CW_(min), CW_(max), and TXOP that are described above, whichare EDCA parameters, are adjusted and thus the priority control inaccordance with the access category is performed, the priority controlbetween the downlink data frame and the trigger frame is necessary forevery access category. For example, in the case of a first configurationin which individual CSMA/CA control is performed, for every accesscategory, on the downlink data frame and the trigger frame, an EDCAparameter, at which the downlink data frame or the trigger frame thathas the greater number of transmission-waiting frames or a larger amountof transmission-waiting data easily acquires a channel access right, isset for every access category. The details will be described below withreference to FIG. 11.

Furthermore, in the case of a second configuration in which commonCSMA/CA control is performed, for every access category, on the downlinkdata frame and the trigger frame, a selection unit is provided in such amanner that, for every access category, the downlink data frame or thetrigger frame that has the greater number of transmission-waiting framesor a larger amount of transmission-waiting data is selected and theCSMA/CA control is performed. The details will be described below withreference to FIG. 12.

FIG. 11 illustrates the first configuration of the access control unit15.

In FIG. 11, an uplink and downlink transmission management function unit100 inputs the downlink data frame in the AP, and the trigger frameinstructing to perform the uplink simultaneous transmission sums up anumber of frames and data amounts for every access category, inputs thedownlink data frame into a downlink data frame access control unit 20,and input the trigger frame into a trigger frame access control unit 30.

The downlink data frame access control unit 20 has a configuration thatis stipulated in IEEE 802.11e, and is configured with a downlink dataframe access category mapping unit 21, transmission queues 22-1 to 22-4and CSMA/CA control units 23-1 to 23-4, each of which correspond toaccess categories, respectively, and a collision avoidance processingunit 24. The downlink data frame access category mapping unit 21 insertsthe downlink data frame into the transmission queues 22-1 to 22-4 inaccordance with the access categories, respectively. In the CSMA/CAcontrol units 23-1 to 23-4, access control is performed on the downlinkdata frame that waits in each transmission queue, in order of prioritythat is based on the EDCA parameter in accordance with the accesscategory.

The trigger frame access control unit 30 has the same configuration asthe downlink data frame access control unit 20, and is configured with atrigger frame access category mapping unit 31, transmission queues 32-1to 32-4 that correspond to the access categories, respectively, CSMA/CAcontrol units 33-1 to 33-4 that correspond to the access categories,respectively, and the collision avoidance processing unit 24. Thetrigger frame access category mapping unit 31 inserts the trigger frameinto the transmission queues 32-1 to 32-4 in accordance with the accesscategories, respectively. In the CSMA/CA control units 33-1 to 33-4, theaccess control is performed on the trigger frame that waits in eachtransmission queue, in order of priority that is based on the EDCAparameter in accordance with the access category.

It is noted that a default value of the EDCA parameter in accordancewith an access category i may be set, in a common-use manner, forCSMA/CA control units 23-i and 33-i in accordance with the accesscategory i, and that, in the case of the same access category i, forexample a weighting may be applied to the default value of the EDCAparameter in such a manner that the access control of the trigger frametakes precedence. At this point, i ranges from 1 to 4.

Additionally, based on a result of summing up a number of frames anddata amounts in terms of each of the downlink frame and the triggerframe for every access category, the uplink and downlink transmissionmanagement function unit 100 causes the CSMA/CA control units 23-i and33-i in accordance with the same access category i to make an adjustmentof the EDCA parameter at which, with a larger number oftransmission-waiting frames or a larger amount of transmission-waitingdata in transmission queues 22-i and 32-i, the channel access right iseasy to acquire.

The collision avoidance processing unit 24 is common to the downlinkdata frame access control unit 20 and the trigger frame access controlunit 30. When transmission timings overlap due to the access control ofeach access category, the collision avoidance processing unit 24performs the access control of the access category that has a higherpriority, but, for example, may preferentially perform the accesscontrol of the trigger category between the downlink data frame and thetrigger frame in the same access category.

FIG. 12 illustrates the second configuration of the access control unit15.

In FIG. 12, the second configuration has the CSMA/CA control units 23-1to 23-4 of the downlink data frame access control unit 20 and theCSMA/CA control units 33-1 to 33-4 of the trigger frame access controlunit 30 in common with the first configuration.

The uplink and downlink transmission management function unit 100 inputsthe downlink data frame in the AP, and the trigger frame instructing toperform the uplink simultaneous transmission sums up a number of framesand data amounts for every access category, inputs the downlink dataframe into the downlink data frame access category mapping unit 21, andinputs the trigger frame into the trigger frame access category mappingunit 31.

The downlink data frame access category mapping unit 21 inserts thedownlink data frame into the transmission queues 22-1 to 22-4 inaccordance with the access categories, respectively. The trigger frameaccess category mapping unit 31 inserts the trigger frame into thetransmission queues 32-1 to 32-4 in accordance with the accesscategories, respectively. One of the downlink data frames that wait inthe transmission queue 22-i in the access category i and the triggerframe that waits in the transmission queue 32-i is selected through aselection unit 41-i, and, in the CSMA/CA control unit 23-i, the accesscontrol is performed on the selected frame in order of priority that isbased on the EDCA parameter in accordance with the access category i.

Based on the result of summing up a number of frames and data amounts interms of each of the downlink data frame and the trigger frame for everyaccess category, the uplink and downlink transmission managementfunction unit 100 causes the selection unit 41-i in accordance with theaccess category i to select the downlink data frame or the trigger framethat has the greater number of transmission-waiting frames or a largeramount of transmission-waiting data in the transmission queues 22-i and32-i, and causes the CSMA/CA control unit 23-i to perform the accesscontrol. In the first configuration, because the EDCA parameters for theCSMA/CA control units 23-i and 33-i are adjusted, the probability thateach of the downlink data frame and the trigger frame will be selecteddepends on a statistical probability at which the random backoff valuesare the same, but in the second configuration, one of the downlink dataframe and the trigger frame is definitely selected according to thenumber of frames or the data amount at the time of waiting thetransmission.

When the transmission timings overlap due to the access control of eachaccess category, a collision avoidance processing unit 41 performs theaccess control of the access category that has a higher priority. It isnoted that the overlapping of the transmission timings due to the accesscontrol occurs also if there are a trigger frame and a downlink dataframe in different access categories and if there are trigger frames ordownlink data frames in different access categories.

As described above, in the access control unit 15 of the AP, if thetrigger frame is transmitted that is destined for a plurality of STAsthat simultaneously transmit the downlink data frame or the uplink dataframe which is destined for the STA, the trigger frame is transmittedafter the channel access right is acquired based on the CSMA/CA control.On the other hand, also in the STA, if the uplink data frame istransmitted, the uplink data frame is transmitted after the channelaccess right is acquired based on the CSMA/CA control. At this point,for example, if a plurality of STAs that make transmission requests toone AP are present, if each performs the CSMA/CA control, theprobability that the AP will acquire the channel access right decreasesremarkably. In contrast, the simultaneous transmission of the uplinkdata frame by the plurality of STAs cancel the transmission request byeach STA and further make it easy for the AP to acquire the channelaccess right, but this is a case where the trigger frame can betransmitted efficiently.

In the first configuration that is illustrated in FIG. 11, when aweighting is applied to the default value of the EDCA parameter inaccordance with each access category in such a manner that the accesscontrol of the trigger frame takes precedence, the EDCA parameter may beadjusted according to the number of STAs that make the transmissionrequests. For example, if bidirectional traffic occurs, a CW size in theAP is set to be smaller than a default value, or the CW size is set tobe larger than the default value for the STA that is capable of beingconnected to the AP or the STAs performing the simultaneoustransmission, using a beacon frame or other frames on a wireless orwired network, and thus the AP that performs the carrier sensing inorder to transmit the trigger frame for the simultaneous transmissioncan preferentially start the transmission.

Second Embodiment

FIG. 4 is a control sequence according to a second embodiment in thewireless communication system according to the present invention.

FIG. 8 illustrates Steps S21 to S29 as a procedure for control ofsimultaneous transmission according to the second embodiment in thewireless communication system according to the present invention.

In Step S21, the AP collects pieces of station information of the STA 1to STA n necessary for the selection of the STAs performing thesimultaneous transmission and for the control of the simultaneoustransmission and totals collected pieces of station information. Next,in Steps S22 and S23, the AP selects the combination of STAs performingthe simultaneous transmission based on the collected stationinformation, calculates the data transmission efficiency of thesimultaneous transmission, and determines whether the calculated datatransmission efficiency is good or bad. At this point, if it is notdetermined that the data transmission efficiency of the simultaneoustransmission is good, in Step S24, the AP does not perform the controlof the simultaneous transmission in the uplink. The processing describedabove is the same in each of Steps S11 to S14 in the first embodiment,which is illustrated in FIG. 7.

In the present embodiment, if it is determined in Step S23 that the datatransmission efficiency of the simultaneous transmission is good, the APcauses the STA side to acquire the channel access right beforetransmitting the trigger frame instructing to perform the uplinksimultaneous transmission to the STAs performing the simultaneoustransmission.

At this point, when the AP determines that the data transmissionefficiency of the simultaneous transmission is good, in Step S25, the APtransmits announcement frames indicating that the simultaneoustransmission has become possible to the STAs performing the simultaneoustransmission. Among the STAs that receive the announcement frames, theSTA that acquires the channel access right with the carrier sensing andrandom backoff control transmits the request frame to the AP. In anexample in FIG. 4, the STA 1 transmits the request frame. In Step S26,the AP receives the request frame transmitted by the STA which acquiredthe channel access right, in Steps S27 and S28, the AP reselects acombination of STAs performing the simultaneous transmission based oncollected pieces of station information, recalculates data transmissionefficiency of the simultaneous transmission, and determines whether therecalculated data transmission efficiency is good or bad. At this time,if the station information is updated, there is also a case where acombination of STAs different from the combination of STAs that isselected in Step S22 is selected. Furthermore, because the STA thatacquired the channel access right and transmitted the request frame isin an idle status, one of the STAs performing the simultaneoustransmission may be decided definitely.

As a result, if it is not determined that the data transmissionefficiency of the simultaneous transmission is good, in Step S24, the APdoes not perform the control of the simultaneous transmission in theuplink. On the other hand, if it is re-determined that the datatransmission efficiency of the simultaneous transmission is good, inStep S29, the AP generates the trigger frame instructing to perform theuplink simultaneous transmission for the selected STAs performing thesimultaneous transmission, and transmits the generated trigger frame.

It is noted that, when the STA that received the announcement frameacquires the channel access right and transmits a request frame, andwhen the AP that received the request frame intends to transmit thetrigger frame after the SIFS time, the trigger frame can be reliablytransmitted by the channel access right acquired by the STA, and thesimultaneous transmission can be started. Furthermore, when a time ittakes from the AP to receive the request frame and transmit the triggerframe until the STAs complete the simultaneous transmission is assumedand when the NAV is set to other STAs that are not selected as the STAsperforming the simultaneous transmission by the request frametransmitted by the STA or by an RTS/CTS frame transmitted and receivedseparately, the STAs selected by the trigger frame of the AP canreliably perform the simultaneous transmission.

Third Embodiment

FIG. 5 is a control sequence according to a third embodiment in thewireless communication system according to the present invention.

FIG. 9 illustrates Step S30 to S33 in which processing operations by theSTA are performed and Steps S34 to S39 in which processing operations bythe AP are performed, as a procedure for control of simultaneoustransmission according to the third embodiment in the wirelesscommunication system according to the present invention.

The first and second embodiments are the procedures in each of which theAP collects and totals pieces of station information of STAs and selectsthe combinations of STAs performing the simultaneous transmission, butin the third embodiment, a predetermined STA x collects and totalspieces of station information of the STA x itself and other STAs,determines whether or not the simultaneous transmission are possible,and announces a result of the determination to the AP, and the APselects the combination of STAs performing the simultaneous transmissionaccording to the announcement. For example, a case where the STA 1 thatis illustrated in FIG. 1 hears uplink frames of the STA 2 and the STA 3,and collects these pieces of traffic information as pieces of stationinformation. Alternatively, the STA 1 may collect pieces of stationinformation of other STA 2 to STA n using the technique of the AP whichis described in the first embodiment. However, as in the firstembodiment, the AP is also assumed to independently collect pieces ofstation information of the STA 1 to the STA n.

In Step S30, the predetermined STA x collects and totals pieces ofstation information necessary for the selection of the STAs performingthe simultaneous transmission and the control of the simultaneoustransmission. Next, in Steps S31 and S32, the STA x selects thecombination of STAs performing the simultaneous transmission based onthe pieces of station information of the STA x itself and other STAs,calculate the data transmission efficiency of the simultaneoustransmission, and determines whether the calculated data transmissionefficiency is good or bad, and if it is not determined that the datatransmission efficiency of the simultaneous transmission is good,returns to Step S31 to perform recollection of the pieces of stationinformation. On the other hand, if it is determined that the datatransmission efficiency of the simultaneous transmission is good, inStep S33, the STA x transmits the request frame indicating that thesimultaneous transmission is possible to the AP. It is noted that, inthe request frame, pieces of combination information or pieces ofstation information of the STAs performing the simultaneoustransmission, a request for the acquisition of the channel access rightto the AP, and a request for including the STA itself in themultiple-user simultaneous transmission in the uplink direction may beincluded. Furthermore, when the STA x knows that QoS data frames of theSTA itself and other STAs occur, the STA x may transmit the requestframe to the AP.

On the other hand, in Step S34, the AP collects pieces of stationinformation necessary for the selection of the STAs performing thesimultaneous transmission and for the control of the simultaneoustransmission from among the STA 1 to STA n and totals collected piecesof station information. When in Step S35, the request frame is receivedfrom the STA, in Steps S36 and S37, the AP selects a combination of STAsperforming the simultaneous transmission based on collected pieces ofstation information, calculates data transmission efficiency of thesimultaneous transmission, and determines whether the calculated datatransmission efficiency is good or bad. At this time, if combinationinformation or station information of the STAs performing thesimultaneous transmission which is determined in the STA is included inthe request frame that is transmitted by the STA, the combinationinformation and the station information may be used in conjunction withthe station information collected by the AP for the processing thatselects the combination of STAs performing the simultaneoustransmission. Furthermore, if the station information is updated, thereis also a case where a combination of STAs different from thecombination of STAs that is selected in Step S31 is selected.

As a result, if it is not determined that the data transmissionefficiency of the simultaneous transmission is good, in Step S38, the APdoes not perform the control of the simultaneous transmission in theuplink. On the other hand, if it is determined that the datatransmission efficiency of the simultaneous transmission is good, inStep S39, the AP generates a trigger frame TRG instructing to performthe uplink simultaneous transmission for the selected STAs performingthe simultaneous transmission, performs carrier sensing and the randombackoff control to acquire the channel access right, and then transmitsthe trigger frame.

It is noted that, if processing operations in Step S30 to S33 in the STAare excluded, processing operations in Step S34 to S39 in the AP arebasically the same as those in Steps S11 to S15 in the first embodiment.In the present embodiment, it is determined whether or not thesimultaneous transmission is possible based on the pieces of stationinformation collected by a predetermined STA x, and then the combinationof STAs performing the simultaneous transmission is finally selectedusing the pieces of station information collected by the AP, or usingthe pieces of station information in conjunction with the combinationinformation or the station information of the STAs performing thesimultaneous transmission which is determined by the STA x. Thus, aprocessing load on the AP can be reduced.

Fourth Embodiment

FIG. 6 is a control sequence according to a fourth embodiment in thewireless communication system according to the present invention.

FIG. 10 illustrates Steps S40 to S43 in which processing operations bythe STA are performed and Steps S44 to S49 in which processingoperations by the AP are performed, as a procedure for control ofsimultaneous transmission according to the fourth embodiment in thewireless communication system according to the present invention. It isnoted that processing operations in Step S40 to S42 and S44 to S48 inthe fourth embodiment are the same as those in Steps S30 to S32 and S34to S38 in the third embodiment, and processing operations in Steps S43and S49 are different from those in Steps S33 and S39 in the thirdembodiment.

When it is determined in Step S42 that the data transmission efficiencyof the simultaneous transmission is good, in Step S43, a predeterminedSTA x generates the request frame indicating that the simultaneoustransmission is possible, acquires the channel access right byperforming the carrier sensing and the random backoff control, and thentransmits the generated request frame to the AP. The request frame, likethe request frame that is transmitted by the STA 1 to the AP in thethird embodiment, may include the combination information or the stationinformation of the STAs performing the simultaneous transmission. On theother hand, if it is redetermined in Step S47 that the data transmissionefficiency of the simultaneous transmission is good, in Step S49, the APgenerates the trigger frame instructing to perform the uplinksimultaneous transmission for the selected STAs performing thesimultaneous transmission, and transmits the generated trigger frame.

In this manner, like in the second embodiment, in the fourth embodiment,based on the channel access right acquired by a predetermined STA x, theAP transmits the trigger frame. Therefore, in the same manner as in thesecond embodiment, when the STA acquires the channel access right andtransmits a request frame, and when the AP that received the requestframe intends to transmit the trigger frame after the SIFS time, thetrigger frame can be reliably transmitted by the channel access rightacquired by the STA, and the simultaneous transmission can be started.Furthermore, when a time it takes from the AP to receive the requestframe and transmit the trigger frame until the STAs complete thesimultaneous transmission is assumed and when the NAV is set to otherSTAs that are not selected as the STAs performing the simultaneoustransmission by the request frame transmitted by the STA or by theRTS/CTS frame transmitted and received separately, the STAs selected bythe trigger frame of the AP can reliably perform the simultaneoustransmission.

In the first to fourth embodiments described above, the procedure forthe simultaneous transmission from the plurality of STAs to the uplinkdirection is described, but if there is the downlink data frame in theAP that is transmitted to the STA, the transmission in the downlinkdirection and the simultaneous transmission in the uplink direction maybe performed successively. For example, in the first to fourthembodiments described above, if the AP starts control of thesimultaneous transmission in the uplink direction, the presence orabsence of the downlink data frame is determined, and if the downlinkdata frame is not present, the trigger frame is transmitted as in eachembodiment and the simultaneous transmission is performed on the STAselected in a combination of STAs performing the simultaneoustransmission. On the other hand, if the downlink data frame is presentin the AP, the transmission of the trigger frame may be performed insuccession to the transmission and reception of the downlink data frameand the ACK. In this case, a combination of the STA that is adestination in the downlink direction and the STAs performing thesimultaneous transmission in the uplink direction is set to be incommon, and the downlink data frame and the trigger frame may betransmitted in conjunction with each other and the ACK in the downlinkdata frame may be transmitted in conjunction with the data frame in theuplink. Alternatively, the transmission of the downlink data frame maybe performed in succession with the transmission of the trigger frame bythe AP and the uplink simultaneous transmission by the STA. In the caseof the successive processing, a period of time when the channel accessright that is acquired in the AP or the STA is transmitted and receivedis assumed.

In the first and third embodiments described above, with the triggerframe, the NAV that prevents neighboring stations from performing thetransmission can be set. The length of the NAV period that is set atthis point is set based on pieces of station information that arecollected. Several methods of setting or revising the NAV areconsidered.

(1) With the trigger frame, the transmission of the data frame is simplyrequested without setting the NAV. In this case, before the STAtransmits the data frame, the STA can transmit an RTS frame and the APcan reply with a CTS frame and start to transmit the data frame.

(2) The NAV is set by performing polling that uses the trigger frame orthe RTS frame for the STA that can be a destination. In this case, withthe trigger frame or the RTS frame, the NAV is set for neighboringstations, and data frames are collected from one or more STAs. Lastly,the trigger frame is retransmitted, leading to the simultaneoustransmission.

(3) The trigger frame or the RTS frame that includes a plurality ofdestination addresses, a response to which is requested by the AP, istransmitted, and the NAV is set for neighboring stations. The STAs, eachof which is designated with a destination address of the trigger frame,may further be caused to provide the responses to the trigger frames inorder or to provide the response to the trigger frames simultaneouslyusing a multiple access scheme, and thus a change in the length of theNAV period may be designated. Lastly, the trigger frame isretransmitted, leading to the simultaneous transmission.

(4) A first trigger frame is transmitted as the trigger frame, it ischecked that the designated STA replies with a second trigger frame, athird trigger frame is further transmitted, and the data frame isreceived from the STA that replies with the second trigger frame. Withthe first trigger frame, the length of the NAV period from pieces ofstation information that are collected is set for neighboring stations,but in the present method, alternatively, a length of the NAV period,which is decided in advance, is set. The STA receives the first triggerframe, and transmits the second trigger frame. At this time, a pluralityof STAs may transmit the second trigger frames simultaneously, maytransmit the second trigger frame at a timing scheduled in a designatedtime by the first trigger frame, may transmit the first trigger frame tothe STAs, one after the other, and may reply with the second triggerframe in order. The AP transmits the third trigger frame for providingan instruction that the STA which normally receives the second triggerframe perform the transmission. On this occasion, with the third triggerframe, the change in the length of the NAV period may be designatedbased on the station information that is included in the second triggerframe, or the combination of STAs that can normally transmit the secondtrigger frame. At this point, with the first trigger frame and thesecond trigger frame, the NAV may be set in the same manner as in theexchange between the RTS and CTS, and the NAV of the neighboringstations for which the first trigger frame is set may be canceled if thethird trigger frame is not transmitted. The third trigger frame mayinclude information, as a synchronization signal, necessary for the STAsperforming the simultaneous transmission, and may have a function astransfer of a transmission right. If the third trigger frame functionsas the transfer of the transmission right, the third trigger frame maybe transmitted after performing the transmission of the data frame inthe downlink direction on a single STA or a plurality of STAs, withoutthe third trigger frame being transmitted immediately after the secondtrigger frame is received.

In the second and fourth embodiments described above, with the requestframe that is transmitted by the STA, the NAV that prevents theneighboring stations from performing the transmission can be set. Atthis point, a value of the length of the NAV period that is set is avalue, which is announced in advance by the AP, or is calculated from alength necessary for the data frame that the STA wants to transmit.Several methods of setting or revising the NAV are considered.

(1) The request frame requests the transmission of the trigger framewithout setting the NAV. In a sequence after the transmission of thetrigger frame, the communication can be performed with the three methodsthat are described in the first and third embodiments described above.

(2) The transmission of the trigger frame is requested while the NAV isset by performing the polling that uses the request frame. In this case,with the request frame, the NAV is set for neighboring stations, and theAP is caused to transmit the trigger frame. On this occasion, in the AP,according to the information, such as the length of the NAV period thatis designated by the STA, the combination of STAs that perform themultiple-user simultaneous transmission in the uplink may be decided orchanged. After the transmission of the trigger frame, the communicationcan further be performed with the three methods that are described inthe first and third embodiments described above. Because the NAV is setone time with the request frame, the length of the NAV period can bechanged with subsequent communication.

An MCS index that indicates the modulation method and the coding ratewhich are used for the user data in the first to fourth embodimentsdescribed above, for example, can be decided in the AP or the STA asfollows. The MCS index is decided taking into consideration a result ofthe communication so far, but can be decided in view of the penalty dueto the performing of the multiple-user simultaneous transmission. If thedecision is made taking into consideration the result of thecommunication so far, the decision can be made in such a manner that theMCS index at which the communication succeeds under the condition thatthe multiple-user simultaneous transmission be the same or in such amanner that an MCS index that has the smaller number of bits per dataframe than the MCS index at which the communication fails under thecondition that the multiple-user simultaneous transmission be the same.If the penalty due to the multiple-user simultaneous transmission isused, for the MCS index that is used when single user communication isperformed, the decision is made using the number of STAs that aremultiplexed due to the multiple-user simultaneous transmission, or usingan access type for multiple-user simultaneous transmission and thenumber of STAs that are multiplexed. The access type, for example isFrequency Division Multiple Access (FDMA), Spatial Division MultipleAccess (SDMA) (or MU-MIMO), or a multiple access scheme that uses both.It is considered that, in the case of FDMA, the communication qualitydecreases due to inter-user interference that results from frequencydeviation and that, in the case of the MU-MIMO, the communicationquality decreases due to inter-user interference that occurs from theincompleteness of spatial signal demultiplexing. Because of this, theMCS index has to be changed as much as the communication is degraded, insuch a manner as to correspond to the small number of bits. Generally,MU-MIMO is greater in penalty than FDMA. As examples of a method ofdeciding the MCS index that is used by the STA in the data frame, thefollowing methods are considered.

(1) The number of multiplexed users and a method of user multiplexingare announced from the AP, and in the STA, from the information, the MCSindex is decided that corresponds to the number of bits which is smallerthan in the case of single user communication, with reference to thepenalty from a table that is stored in advance.

(2) The number of multiplexed users and the method of user multiplexingthat are used in the AP are estimated, and from the number ofmultiplexed users and the method of user multiplexing that are assumed,the MCS index is decided that corresponds to the number of bits that issmaller than in the case of the single user communication, withreference to the penalty from the table that is stored in advance.Furthermore, when it comes to deciding the penalty, the penalty for auser combination can also be calculated from a value of correlation ofpropagation characteristic information on a channel status to the STA.

(3) The penalty due to the multiple-user simultaneous transmission isannounced from the AP, and the MCS index is decided that corresponds tothe number of bits which is smaller than in the case of the single usercommunication.

(4) The MCS index that is used for the multiple-user simultaneoustransmission is announced from the AP, and the designated MCS index isused.

As a specific index of the penalty, a value indicating the extent towhich the number of bits has to be decreased according to an option ofbeing able to select the MCS index that can be used can be used, or avalue that results from quantizing an amount of decrease insignal-to-interference-plus-noise ratio (SINR) or quantizing 1 orsmaller or a value in the digital form can be used. For example, ifbidirectional communication in the uplink using MU-MIMO is performed ontwo STAs, it can be announced that the MCS index is lowered by one andit can be announced that the SINR is lowered by 2 dB.

The many features and advantages of the embodiments are apparent fromthe detailed specification and, thus, it is intended by the appendedclaims to cover all such features and advantages of the embodiments thatfall within the true spirit and scope thereof. Further, since numerousmodifications and changes will readily occur to those skilled in theart, it is not desired to limit the inventive embodiments to exactconstruction and operation illustrated and described, and accordinglyall suitable modifications and equivalents may be resorted to, fallingwithin the scope thereof.

What is claimed:
 1. A wireless LAN access point in a wirelesscommunication system in which one wireless LAN access point (which ishereinafter referred to as an “AP”) and a plurality of wireless LANstations (each of which is hereinafter referred to as an “STA”) areconnected to each other, and in which an uplink data frame issimultaneously transmitted from each of the plurality of STAs to the APin a multiple access scheme, the wireless LAN access point comprising: astation information collection unit that collects from the plurality ofSTAs station information which is used for selection of STAs performingsimultaneous transmission and for control of the simultaneoustransmission; a simultaneous-transmission determination unit thatselects a combination of STAs performing the simultaneous transmissionbased on the station information; and a trigger transmission unit thattransmits to each of the STAs, which simultaneously transmits the uplinkdata frame, a trigger frame which instructs to perform the simultaneoustransmission and which includes information necessary for the control ofthe simultaneous transmission and a modulation and coding scheme used inthe simultaneous transmission; wherein the trigger transmission unitselects the modulation and coding scheme that corresponds to a smallernumber of bits than in the case of a single user communication.
 2. Awireless LAN station in a wireless communication system in which onewireless LAN access point (which is hereinafter referred to as an “AP”)and a plurality of wireless LAN stations (each of which is hereinafterreferred to as an “STA”) are connected to each other, and in which anuplink data frame is simultaneously transmitted from each of theplurality of STAs to the AP in a multiple access scheme, the wirelessLAN station comprising: a station information collection unit thatcollects from the plurality of STAs station information which is usedfor selection of STAs performing simultaneous transmission and forcontrol of the simultaneous transmission, and that transmits thecollected station information to the AP; a trigger reception unit thatreceives a trigger frame which instructs to perform the simultaneoustransmission, which includes information necessary for the control ofthe simultaneous transmission and a modulation and coding scheme used inthe simultaneous transmission, and which is transmitted to the STAsperforming simultaneous transmission selected by the AP according to thestation information, wherein the modulation and coding schemecorresponds to a smaller number of bits than in case of a single usercommunication; and a wireless frame transmission unit that transmits theuplink data frame to the AP by using the modulation and coding schemeincluded in the trigger frame.